Momentary venting means for poweroperated percussive tool



N. AKERMAN 3,034,302

MOMENTARY VENTI NG MEANS FOR POWER-OPERATED PERCUSSIVE TOOL May 15, 1962 2 Sheets-Sheet 2 Filed March 28, 1960 FIGS INVENTOR.

NIGEL AKER MAN Xld/W TTORNEY MOMENTARY VENTENG MEANS FOR POWER- OPERA'IED PERCUSIVE TOOL Nigel Akerman, Baltimore, Md., assignor to The Black and Deelrer Manufacturing (Iompany, Towson, Md., a corporation of Maryland Filed Mar. 28, 1960, Ser. No. 18,178

1 Claim. (Cl. oil-62.5)

The present invention relates to a power-operated percussive tool having pneumatic driving and ram retraction means, and more particularly, to such a tool having improved means for the momentary venting of the mass of air in an entrapped air chamber formed between a pair of telescoping reciprocating members.

In the prior art, numerous power-operated percussive tools, generally in the form of portable electric hammers, have been constructed in which there is a telescoping reciprocating ram and piston having an imperforate entrapped air chamber therebetween, the purpose of the entrapped air chamber being to provide either an air cushion serving a function such as may be supplied by a pneumatic shock absorber, or else to provide a suitable air spring that supplants the conventional spring that is ordinarily provided in most portable electric hammers. The function of the air spring is twofold: not only to drive the ram ahead of the driving piston by means of a compression of air therebetween, but also, to retract the ram away from the tool bit by means of a suction effect created by the retracting piston and the resultant subatmospheric pressure in the entrapped air chamber. These alternate compression and suction eifects exhibited by the entrapped air for the alternate driving and retraction of the ram, respectively, have long been known in the art; and there are many constructions which have been devised.

Apropos thereto, one problem in particular that has been brought into focus concerns the momentary venting or 'porting of the entrapped air to atmosphere so as to compensate for inherent leakages in the mechanism and thus allow for an equalization of the mass of entrapped air, that is to say, the mass of air in the entrapped air chamber will be allowed to adjust to a substantially constant worle'ng level during the operation of the tool. Several solutions to this problem have been offered over the years, as for example, in the German Patent 285,399 issued to Christiansen in 1915, in which the mass of entrapped air is allowed to vent (at certain times) to the atmosphere by means of a longitudinal passage within the piston in combination with communicating radial canals and an external annular recess in the piston, the latter annular recess in turn registering with ports in the outer telescoping member. Another example is the United States Patent 2,880,585 issued to Badcock in 1959, in which the mass of entrapped air communicates with the atmosphere by means of an internal annular recess in the outer ram member in cooperation with at least one longitudinal surface groove formed on the external surface of the inner piston member.

Each of these latter specifically enumerated constructions, as well as numerous others that could be cited equally as well, are provided with an inner telescoping reciprocating member, usually the piston, which invariably is relatively long or else is provider with a relatively long skirt. xperience has shown that such a long or long-skirted (and hence heavy) piston member sulfers from several critical defects, among which the most important are as follows: First, a long-skirted piston necessarily entails a great deal of Wear contact between the mating wall surfaces of the telescoping members as they reciprocate with respect to each other; this sliding contact invariably creates minute scratches or burrs r imperfections in the highly-polished mating wall surfaces.

3,%34,32 Patented May 15, 1962 These imperfections in turn tend to tear the conventional sealing rings which are placed upon the external surface of the piston, thus lowering the working efficiency of the tool and ultimately leading to a complete failure. Secondly, such a long-skirted piston is necessarily heavy and adds to the weight that must be driven by the motor; it is well-recognized that for best results, the unbalanced mass driven by the motor should be minimized. Thirdly, in order to allow for a momentary venting of the mass of entrapped air, proper communication to atmosphere must be provided, thus necessitating perhaps a longitudinal passage in combination with radial canals and an external annular recess, or perhaps a series of longitudinal surface grooves in combination with an internal annular recess in the outer member, as hereinbetore stated. Such constructions are necessarily complicated and hence expensive to manufacture.

Accordingly, it is an object of the present invention to provide an improved structure that alleviates these aforementioned deficiencies.

It is another object of the present invention to provide a simple and rugged structure that is easy and inexpensive to manufacture. g

It is still another object of the present invention to provide improved momentary venting means of the mass of entrapped air.

In accordance with the teachings of the present invention, a power-operated percussive tool is provided having a pair of telescoping members reciprocating with respect to each other and constituting an outer member and an inner member having an entrapped air chamber therebetween. One of these telescoping members, preferably the outer member, is the ram or striker, While the other of these telescoping members, preferably the innermember, has the driving piston. Momentary venting means are provided to allow the mass of air in the entrapped air chamber to adjust to a substantially constant working level during the operation of the tool, such means taking the form of a disc-shaped relatively short piston formed on the inner end of the inner member and confining one end of the entrapped air chamber and adapted to cooperate, at various appropirate times, with an internal annular recess formed inthe wall of the outer member. The width of the internal annular recess is chosen to be slightly greater than the height of the relatively short disc-shaped piston so that the mass of entrapped air may communicate with the atmosphere for proper venting whenever the piston passes by the internal annular recess.

Other objects of the present invention will become apparent from the following specification taken in conjunction with the enclosed drawings, in which:

FIGURE 1 is a pictorial view of the type of portable electric hammer which may feature the teachings of the present invention;

FIGURE 2 is a partial longitudinal section taken along the lines 22' of FIGURE 1 and showing the piston telescoped Within the hollow cylindrical ram;

FIGURE 3 is a partial longitudinal section similar to that of FIGURE 2, but showing the piston withdrawn past the internal annular recess formed within the ram;

FIGURE14 is a cross-sectional view taken along the lines 44 o'i-FIGURE 2;

FIGURE 5 is a cross-sectional viewtaken along the lines 5S' of FIGURE 3;

FIGURE 6 is a cross-sectional view taken along the lines 66 of FIGURE 3; and I FIGURE 7 is an enlarged view of a portion of FIG- URE 2 showing the piston as it passes by the internal annular recess for momentary venting purposes.

With particular reference to FIGURE 1, there is illustrated a typical portable electric hammer It in which the teachings of the present invention may be incorporated.

It will be appreciated, of course, that the present invenhandle 12 ,linecord'1i3, amain barrel or housing 14,-

anda suitable tool bit 15. With particular reference to FIGURE 2, there is illus trated a hollow cylindrical'striker or ram 16 having a closed forward end 17, which is adapted to impact against the tool bit 15in a manner well-known in the art and hence not illustrated herein. a The ram 16 can reciprocate within a suitable barrel or sleeve 30 as guided on conventional lands 18 having between'them suitable vents 19 to precludean adverse air pocket from being created. Sleeve 30' is secured within the housing 14 by means of threads 31,'andit will be appreciated by those skilled in the art that the housing l and sleeve 30 may be in tegrally formed, if desired. 7 r

A disc-shaped relatively-short piston member 20 is telescoped within the-ram 16 and has an integral (or otherwise suitably secured) piston rod 21. The piston rod 21, as illustrated, is adapted to be reciprocated by meansof a crosshead 22 and connecting-rod 23, the latter being joined to a suitable crank (which being conventional has been-omitted-for ease of illustration), It be understood, naturally, that other means of so driving the reciprocating piston member 20 could be employed without de parting from the essence of the present invention. Morteover, as shown in FIGURES 1 and-2, the crosshead 22 and the ram 16 areeach guided within housing 14 Sep As shown most clearly in FIGURE 3, piston member 26 v is provided with an external annular groove 24 (axially centered approximately with respect to the axial height of the piston member 20, as shown most clearly in FIG- URE 7) into'which is mounted aconventional resilient sealing ring'25 made of rubber or other suitable material.

Only one such-sealing'ring 25 has been illustrated for clarity of understanding, but it will be obvious to those skilled in the art that additional sealing: rings could be provided for additionalsealing effect, if desired;

ing of the entrapped air to atmosphere whenever piston member 20 passes by internal annular recess 28. The actual radial depth of the internal annular recess 28 can be in the order of 0.003 inches, but is exaggerated herein for ease of illustration. The radial dimensions of sealing ring 25 are chosen for proper and efficient sealing between the piston member Ztl'and ram .16 in a manner well known in the art, yet not such that the sealing ring 25 will preclude proper venting as it passes by the intern-a1 annular recess 28. Also 'a -bevel 29 is provided on the edges of internal annular recess 28 to preclude the possi-- bility of sealing ring 27 being torn as piston member 20 passes by internal annular recess 28. It will be appreciated th-at in the drawings, say FIGURE 7, certain di mensions have been somewhat exaggerated for ease of illustration and clarity of understanding (and protruding slightly beyond the circumference of piston member 20 As shown in FIGURES 2 and 3, the space between the piston member 20 and the closed forward end 17 of ram In order to allow this mass of entrapped air to coma pensate for inherent leakagesand to equalize, that is to sayf to adjustto a substantia-lly constant working level, momentary venting or porting-meansare provided so as to allow the mass of entrappedjair to communicate with the atmosphere at certain times during the operating cycle of the tool. It willbe' appreciated that the space 27 on 1 the other side of the piston member 20 opposite from the entrapped air chamber 24, may for all intents and'purposes be considered as substantially equivalent to atmospheric pressure. With this in mindgthe momentary vent- I ing means of the present invention will now be described. As shown in FIGURES 2 and 3, and more'clearly in FIGURE 7, an internal annular recess28 is formed within theram- 16; and the (axial) width A of the internal annular recess 28 is slightlygreater than the (axial) height B of the relatively shortdisc-shaped piston member 20 (see FIGURE 7-) thus allowing for a momentary ventas shown in FIGURE 7). a

It is seen that the present invention fulfills aneed for a light-weight driving piston having a minimum of surface wear contact with the mating surfaces of the ram and having convenient means for the proper momentary venting of the mass of entrapped air, in an overall construction which is ideally suited for an easy and economical production. I

Obviously, various-minor modifications may be made without departing from the basic spirit of the present invention. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced other than is specifically described.

I claim: I V

A power-operated percussive tool, comprising a housing including a cylindrical barrel, a floating ram guided for reciprocation within said barrel, said ram comprising a hollow cylindrical member having a closed forward end, a telescoping piston guided for reciprocation within said ram, said piston including an elongated piston rod and further including a disc-shaped relatively-short piston member secured to the forward end of said rod and guided within said ram, said piston member and said closed forward'end of said ram having a chamber wherein air may be entrapped therebetween, means for communicating to atmosphere the remaining portion of said barrel on the side of said piston member opposite from said chamber, a cross-head secured to the opposite end of said rod, means independent of said ram to guide said crosshead for reciprocation within said barrel, power-operated protruding slightly beyond the circumference of said piston member, and said ram havingan internal annular recess formed therein, said internal annular recess having annular edges which are beveled in a direction away from saidrecess, and the axial width of said internal annular recess beinggreater than the axial height of said disshaped piston member, whereby said ram alternately will be advanced and retracted by the alternate compression and suction effects experienced by the entrapped air in said chamber, and whereby as said piston and ram reciprocate with respect to each, a momentary venting of the entrapped air in said chamber may occur whenever said piston mem berpassesby and is in communication with said internal annular recess 7 References Cited in the file of this patent UNITED STATES PATENTS 1,610,580 Nicholson Dec. 14, 1926 2,396,155 Christensen Mar. 5, 1946 r 2,444,586 1 Wuensch Julyfi, 1948 2,561,009" Byers'et a1 July 17, 1951 2,880,585 B-adcock Apr. 7, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,034,302 May 15, 1962 Nigel Akerman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 63, for "provider" read provided column 2, line 42, for "appropirate" read appropriate column 3, line 46, for "material." read material, (and protruding slightly beyond the circumference of piston member 20 as shown in FIGURE 7) column 4, lines 16 to 18, strike out '(and protruding slightly beyond the circumference of piston member 20 as shown in FIGURE 7)"; lines 49, 59 and 60, for "dis-shaped", each occurrence, read disc-shaped Signed and sealed this 9th day of October 1962.

(SEAL) Attcst:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

